1. Field of the Invention
The invention relates to a device for rotating a disc-shaped information carrier, which device comprises a frame, a turntable which is rotatable about a shaft and is journalled relative to the frame by means of a radial bearing, the turntable having a supporting surface for the information carrier, and an electromagnetic drive unit comprising a stator section secured to the frame and a rotor section secured to the turntable.
2. Description of the Related Art
A device of the type referred to above is known from British Patent Application GB 2,180,413. The known device is intended in particular for rotating hard discs for data storage and is used in a scanning system comprising a scanning unit. The device comprises a d.c. motor having a stator with stationary coils and a rotor with permanent magnets. The rotor is secured to a rotor shaft which is rotatably supported relative to the stator by means of two ball-bearings. The rotor shaft carries a turntable for supporting the hard disc. A drawback of the known device is that the bearing arrangement used therein may give rise to impermissible wobbling of the rotor shaft and the turntable secured thereto. In particular, comparatively large irregular excursions (non-repeatable runouts) of the turntable in a radial and, particularly, in an axial sense may arise owing to ball-bearing faults, which are caused for example by out-of-roundness of the balls or by deformed ball tracks. The resulting undesirable excursions by nature often fall beyond the control range of the scanning system, so that the scanning unit may collide with and thereby damage the hard disc.